Photoconductive cell



April 6, 1954 R. L. SMALL 2,674,700

- mno'roconouc'rxvz cm.

Filed Sept. 22. 1952 III- lm1 INV TOR P.L.5 ALL BY 05M Patented Apr. 6,1954 7i l i. h a. Fireye Corporation, Boston llass la corpora- 1";i'ifi'rfii iiifr is sacral: uni e J it; appli ati n September :2.measuremen 1W5 f a 1 clam; crass-sis). it: Q's-" 5. 1". r,- i if; .1-

" -3- This invention relates to a new-and improved it that thcsetoelectric cells prebead-type photo-conductive cell which is pari sentasubstsntially'wide angle'responseto-pol ticlfllrly adaptable flliherical response sible' iire" sources. I! the novel "cell hereof ls Aprincipal object of this invention is to admountedon a wall orceiling ofa room which is NIT D,S TES vantageously adapt prior art end-onbead-type "g to besupervisedior firefi'a relatively largerephotoconductive cells for hemispherical response. spouse is providedtoradiation traveling substan.

Anotherobiect of this invention isto obtain .a tialiy in' the plane ofthe photoconductive marelatively uniform hemispherical response fromterialJ The end-on bead-type photoconductive bead-type photooonductivecells. cell'is "incapable of provlding -'this type of re- 7 Anotherobject of this invention is to provide spouse, for the reasonspreviouslynoted. Ruthera photoconductive cell which is easily adaptable more, toadapt this bead-type structure by applyto both end-on and hemisphericalresponse. inglead sulfide to a dome-type surface in lieu of Anotherobject of this invention is to improve a fiat surface, would highlycomplicate the fabrithe operating stability ofbead-typephotoconduccation processes for the cells', -and. at the same tivecells. a p is time. would greatly increase thecost thereof. 1

Heretofore, photoconduetive cells generally The photoconductive cellhereof utilizes as a utilized in commercial installations have combasicand major subcomponent the end-on cell prised the characteristichermetically sealed enpreviously described. lLmoyel ieamr-g eqntem;velope typical of most vacuum tubes. With the plates a special-typecylindrical lens having further development of photoconductiv mago Thisrecess has terials. such as lead sulfide, the art has advanced Walldefined by rotating a particular parabolic to th point whereinphotoconductive materials segment about its latus rectum. The lens iscan be satisfactorily applied or otherwise declosely coupled to thephotoconductive surface posited on an external or outer surface of arelawhereby radiation emanating from sources other tively small solidhead which acts as a support for 2:, than at an angle which issubstantially normal to this material. If the necessary electricalconnecthe flat surface of the photoconductive material tions are made tothe photoconductive material is reflected by the walls of this recess,so as to imthrough the use of terminal pins or lead wires, a pinge at asubstantially normal angle upon the satisfactory photoconductive cellresults. Furphotoconductive material which is preferably lothermore, ifthe applied photoconductive material cated a defined distance from thefocal point of is effectively isolated from ambient gases, particthelens. I

ularly oxygen and water vapor, a cell of this con- In order that thefeatures of this invention and struction is generally superior tophotoconducthe mode of operation thereof may be readily untive cellsconstructed of the same materials 10- derstood,adetailed descriptionfollows hereinafter cated within hermetically-sealed envel pes. withparticular reference being made to the draw- Because of the relativeease in applying photoings wherein: conductive materials to flatsurfaces, the bead- Fig. l is a perspective view of the basic end-ontype photoconductive cells recently introduced bead-type photoconductivecell:

have generally a fiat surface to which a hat layer Fig. 2 is a plan viewof the active suriaceof the of lead sulfide is applied. Thisconfiguration photoconductive cell shown in Fig. 1;

therefore naturally presents maximum sensitivity Fist-3 is a perspectiveview of the-novel phototo radiation which impinges at a normal axis toconductive cell hereof showing the lens with its the plane of said leadsulfide. If this radiation Parabolic recess; f

deviates from this normal axis, the response ob- Fig. 4 is aside-elevational view of the phototained from the cell varies in theusual cosine 5 c0nductivccc11sh0Wn1nH8- nd manner, whereby this type ofcell construction, Fig. 5 is a side-elevations! view of the parabolicfor all practical purposes. presents a negligible lens hereof, togetherwith a graphical diagram sensitivity to radiation emanating from sourcesof assistance showing the principles involved in which lie in the planeof said lead sulfide layer. 7 constructing the parabolic recess thereof.

This directional response characteristic pre- Referring now generally toFigs. 1 and 2, a pre.

vents the use of these bead-type photoconductive ferred embodiment of anend-on bead-type photo;-

cells in many applications for which they would conductive cellcomprises, for example, a glass or otherwise be highly satisfactory. Forexample, ceramic body 6 having a disc-shaped upper perin certain typesof fire detectors wherein phototion I and a cylindrical lower supportingportion electric cells are utilizedto detect flame radiation, 6.3 8.From a generic aspect. however, this beads-.-

3 type body may assume any shape that is capable or supporting a layeroi photoconductive material. However, inasmuch as the invention hereofcomprises and is applicable to end-on beadtype cells, the body usedshould have at least one relatively flat surface. to which is appliedthe activated photoconductive material. In the usual instancailt'vsilibohbbvious'that chum-action of the eell'can be simplified and aiao bemade It should be understood. however, that parabolic segment It, aswell as the entire inverted recess. is constructed by rotating segmentI1 about the latus rectum for the parabola of which segment i! is aportion.

Parabolic segment I! forms a portion oi the upper half of the parabola1F==4j:z, which is symmetriul'lbqmz the: vertexislocatedoitthewisinlorthesaldrales. The

more cheaply ii the photoconductive material is 10 focal point P islocated a distance i from the applied to such a flat surface.

Point represents the intersection of Metallic pins 9 and it are sealedM440.

,su'ments l6 and ll and is located at that a substantial portion ofeachoi' the'plns 'theextremity of the latus rectum, a distanoe oi trodesthereirom. The uppereeadstsnoislbwniouwzimdecal nine-2.

is covered with a layer oi photoconduotiye g n.

of pins 9 and It are flush of disc portion 1. The top surface of thisportion airf szriaa' I the parabola is therefore intersection oiparabolic Electrodes l2 and I3 mechanically aim!!! M 1 with the sidewall of lens IS. The cally oowle the flush ends of pins 9 and II (notmpointrpoooint'rnrepresenteo rhimklwioiqmomvg aeberhlddrahomby;

unissued betweeirpins: :9 andewiadeteimined princlpallyby thelsmalimaoitphotoaopduotive material "QWQLQGCMSJI 3,1 of llher-photoconduetiveamaten'ai atmit ts the active'iportionoi'rthe cell structure; .flsatiifm. amropriatewelengthscf radiant energy must impinge "filmcause thecharacteristic photoeondnetiue thnpedance change. -exvmodsurtace'otrphotoconductive materifl ii is preia ably --oovered-.;by'aprotectiveoompound whereby the active areawat Allis isolated-delirium-tarv luirwhichtentisto immir-thestabllitywoiithe cell.Electricalcirsuit connections-are madeltozthecollby-insertmg pins-=0 andil-intmmsmall-sizeiemale socket; The'projectinga'imht portion -"|-withrespectto bodyportionw merely-dullitates the manualinsertion-andremoval-ot theoell from m'm and isthereiorenot actuallyremiirodzior the operational thecell. Bycouplin: :lens 46 to the uppersuriaceoi the photoeonduotive oell asshown in Figs. 3 and i,

the angle of response of the cell is increased,

whereby substantially any radiation emanating from any hemisphericalsource will-create .a substantial output response from the-cell. Lensmay be constmctedof any oi the many-optical materials which are wellknown in the. lem or; having at least an index of refraction greaterthan-a minimumvalne hereinaiter-detennined.

This lenshas preferably a cylindrical outer-wall,

whereby a contiguous surface is'presented with respect to projectingorimI. ,An inverted para bolic recess l6 and I! is formed fromlthe-upporsurface; with a principal axis corresponding-em that of theprincipalaxisoithe cylindrical lens; K ine-contours oflthisnlensirom'the baseto the apex oi. the ooniealrecessaredormed lay-rotatingamarabolic segment-aboutthe lotus recmm do A slotted groove 18 is formedinomthebottom suriaoe :of least! whorebsreiectrodes .12 and -l 8' do notdisturb the seating of lens on the upper suni aoe -of portion 1. Lens i5may :be cemented or otherwise mechanically bonded to body 8 by suitableconventional means.

A side-elevational view of lens liis shown in Fig. swim-certaingraphical construction superimposed thereon whereby the principlesinvolved in determining the shapes oi parabolic segments and vi 7 maybereadily understood. .In order to almpliiy the-explanation. only thedesign of unbeliesegment 17 vwill be stated in -.detail.

milli it r? elitism pointT-TIL ment Ills diffused over whereby parallelradiation secsuriacefl; j The radius oi surtace i4 isrepresentediby'rgfivhichdsthe length of'the normal tolatus rectum S1?extended to F1. It should be noted that the-re s-t cm'impinging uponsin-face It" becomes morepmfiuse as surface 14 is elevated towardpoint'sif It it is desiredthatthisradiationhave an extremeconcentration, surface 14 should be located .so that lt passes throughfocalpoln't F; In the usual cell construction, however, concentration orradiation upon a small .I hotocondnctive snriace'is not highlydeslr'able, 'innsmuch as improved cell characteristics-can be obtainedittliis radiation isspreazd uniformly over all of the actlve'area orthe'cell. The index oi refraction oi'the material 'iormlng lensitlshould be such theta ray impinging at point S will have-an angle ofreflection greater than the critical angle, whereby said ray will hereflected and not refracted, t

It is'to be understood thatqthe above-described arrangement. isillustrative of the application of the principles oi this invention, andnumerous otherprrangements may be devised by those skilledin theartwithont; departing from the cone h r ot. f

Iciaim: T J Q 1. A jpliotoiconductive cell comprising ".asup port. alayer-:01 photoconductive material applied to said-airpo and ail ns m cn c ly u e to: mi p orti s d n -theme. n mv rt fl recessiormed by.rotating a. parabollcsegznent aboutfits latusrectum. I I 2. Aphotoconductive cell comprising a support, a'layer o1 photoconductlvematerialapplied to said support, and alens mechanically coupled tosaidsupl said lens having an inserted recess formed by rotating -a parabolicsegment about its 'latus rectum. said photoconductive layer beingpositioned at a normal angle'to said latus rectum.

3. A photoconductive cell;oomprising a support,a.layer-ofphotoconductivematerial applied tosaid support. andalensmechanioallyooupled to. said -suppont,' -sald lens shaving. an invertedrecess formed by rotating a parabolic segment about its latus rectum,said photoconductive layer being positioned at a normal mile to saidlatue rectum and being centrally dispoeed there about.

4. A photoeonduetive cell comprising a support, a layer ofnhotoconductlve material applied to said support, and a lensmechanicallycoupled recele formed by rotating a parabolic segment gem;it: iatm rectum, laid pbotoconductive connections to aid layer ofphotoconductive material, and a lens mechanically coupled to said mort,aaid lena having an inverted receea 6 formed by rotating a parabolicsegment about its latue rectum, said lens being or material having anindex oi retraction such that a ray impinging at the apex of saidinverted receee at 'lielereneeacltedintheflleotthiapatentUNITEDBTATEBPATINI'B Number Name Date 285,497 Dell Dec. 14, 18802,472,879 June 14, 1949 FOREIGN PATENTS I Number Country Date sauceFrance Mar. 21, 1904

